1. Field
The invention relates generally to a sensor for measuring blood pressure and derived hemodynamic parameters, and more particularly to a continuous non-invasive arterial pressure (CNAP) measurement, where the sensor is disposable.
2. Description of Related Art
Blood pressure (BP) may be measured in a number of ways. As one example, a standard non-invasive sphygmomanometer (NBP) may be placed on the upper arm or wrist. The NBP applies pressure to the arteries, causing them to constrict and limit blood flow. As the pressure is released, blood flow is restored in the artery, and the systolic and diastolic blood pressures may be measured. NBP measures BP intermittently and not continuously.
Invasive devices may also be used to measure blood pressure, such as an intra-arterial catheter, for example. Invasive Blood Pressure (IBP) devices can be painful to the patient.
Another device for measuring blood pressure is a sensor having a cuff, an infrared light source, and a light detector for measuring a photo-plethysmographic (PPG) signal. This type of signal is known from pulse oximetry (PO). The PPG-signal is fed into a control system, which produces a counter-pressure in the finger cuff. It is well known that the counter pressure equals intra-arterial pressure when the PPG-signal is kept constant. Thus, the counter pressure, which is indirect equivalent to intra-arterial BP, is measured. This method is known as “Vascular Unloading Technique” or “Continuous Non-Invasive Arterial Pressure” (CNAP). This method combines the advantages of both previous methods NBP and IBP; it delivers continuous BP-information and it is painless due to its non-invasive nature.
A CNAP-sensor system is typically placed over an artery of the human body (e.g. at the finger). The sensor system includes a cuff having air supplies and a PPG system. The PPG system may include at least one light source, at least one light detector, electrical components, and one or more connectors. The sensor system is further connected to a control system, which provides an electrical interface and air supply. For a better light transmission, light coupling systems can be used. When the sensor has to be replaced (e.g. for hygienic reasons) all components have to be replaced. Thus, it would be desirable to create a disposable and detachable sensor system.